1 /* bits.c -- output variable-length bit strings
3 Copyright (C) 1999 Free Software Foundation, Inc.
4 Copyright (C) 1992-1993 Jean-loup Gailly
6 This program is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program; if not, write to the Free Software Foundation,
18 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
24 * Output variable-length bit strings. Compression can be done
25 * to a file or to memory. (The latter is not supported in this version.)
29 * The PKZIP "deflate" file format interprets compressed file data
30 * as a sequence of bits. Multi-bit strings in the file may cross
31 * byte boundaries without restriction.
33 * The first bit of each byte is the low-order bit.
35 * The routines in this file allow a variable-length bit value to
36 * be output right-to-left (useful for literal values). For
37 * left-to-right output (useful for code strings from the tree routines),
38 * the bits must have been reversed first with bi_reverse().
40 * For in-memory compression, the compressed bit stream goes directly
41 * into the requested output buffer. The input data is read in blocks
42 * by the mem_read() function. The buffer is limited to 64K on 16 bit
47 * void bi_init (FILE *zipfile)
48 * Initialize the bit string routines.
50 * void send_bits (int value, int length)
51 * Write out a bit string, taking the source bits right to
54 * int bi_reverse (int value, int length)
55 * Reverse the bits of a bit string, taking the source bits left to
56 * right and emitting them right to left.
58 * void bi_windup (void)
59 * Write out any remaining bits in an incomplete byte.
61 * void copy_block(char *buf, unsigned len, int header)
62 * Copy a stored block to the zip file, storing first the length and
63 * its one's complement if requested.
77 static char rcsid[] = "$Id: bits.c,v 1.4 2006/11/20 08:40:33 eggert Exp $";
80 /* ===========================================================================
81 * Local data used by the "bit string" routines.
84 local file_t zfile; /* output gzip file */
86 local unsigned short bi_buf;
87 /* Output buffer. bits are inserted starting at the bottom (least significant
91 #define Buf_size (8 * 2*sizeof(char))
92 /* Number of bits used within bi_buf. (bi_buf might be implemented on
93 * more than 16 bits on some systems.)
97 /* Number of valid bits in bi_buf. All bits above the last valid bit
101 int (*read_buf) OF((char *buf, unsigned size));
102 /* Current input function. Set to mem_read for in-memory compression */
105 off_t bits_sent; /* bit length of the compressed data */
108 /* ===========================================================================
109 * Initialize the bit string routines.
111 void bi_init (zipfile)
112 file_t zipfile; /* output zip file, NO_FILE for in-memory compression */
121 /* Set the defaults for file compression. They are set by memcompress
122 * for in-memory compression.
124 if (zfile != NO_FILE) {
125 read_buf = file_read;
129 /* ===========================================================================
130 * Send a value on a given number of bits.
131 * IN assertion: length <= 16 and value fits in length bits.
133 void send_bits(value, length)
134 int value; /* value to send */
135 int length; /* number of bits */
138 Tracev((stderr," l %2d v %4x ", length, value));
139 Assert(length > 0 && length <= 15, "invalid length");
140 bits_sent += (off_t)length;
142 /* If not enough room in bi_buf, use (valid) bits from bi_buf and
143 * (16 - bi_valid) bits from value, leaving (width - (16-bi_valid))
144 * unused bits in value.
146 if (bi_valid > (int)Buf_size - length) {
147 bi_buf |= (value << bi_valid);
149 bi_buf = (ush)value >> (Buf_size - bi_valid);
150 bi_valid += length - Buf_size;
152 bi_buf |= value << bi_valid;
157 /* ===========================================================================
158 * Reverse the first len bits of a code, using straightforward code (a faster
159 * method would use a table)
160 * IN assertion: 1 <= len <= 15
162 unsigned bi_reverse(code, len)
163 unsigned code; /* the value to invert */
164 int len; /* its bit length */
166 register unsigned res = 0;
169 code >>= 1, res <<= 1;
174 /* ===========================================================================
175 * Write out any remaining bits in an incomplete byte.
181 } else if (bi_valid > 0) {
187 bits_sent = (bits_sent+7) & ~7;
191 /* ===========================================================================
192 * Copy a stored block to the zip file, storing first the length and its
193 * one's complement if requested.
195 void copy_block(buf, len, header)
196 char *buf; /* the input data */
197 unsigned len; /* its length */
198 int header; /* true if block header must be written */
200 bi_windup(); /* align on byte boundary */
204 put_short((ush)~len);
210 bits_sent += (off_t)len<<3;
215 if (key) zencode(*buf, t);